U.S. patent application number 11/332246 was filed with the patent office on 2007-11-08 for golf ball.
This patent application is currently assigned to BRIDGESTONE SPORTS CO., LTD.. Invention is credited to Atsuki Kasashima, Katsunori Sato.
Application Number | 20070259739 11/332246 |
Document ID | / |
Family ID | 38446493 |
Filed Date | 2007-11-08 |
United States Patent
Application |
20070259739 |
Kind Code |
A1 |
Kasashima; Atsuki ; et
al. |
November 8, 2007 |
Golf ball
Abstract
In a golf ball having, on a spherical surface, numerous dimples
in a plurality of types of differing diameter, the dimples include
smallest size dimples having a diameter of 2.7 mm or less and
largest size dimples having a diameter of 4.3 mm or less. At least
50% of the total number of dimples are dimples in which an arc that
connects mutually opposing positions on a wall of the dimple at a
70% dimple depth level with a deepest position on the dimple wall
has a radius of curvature R of at least 15 mm.
Inventors: |
Kasashima; Atsuki;
(Chichibu-shi, JP) ; Sato; Katsunori;
(Chichibu-shi, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
BRIDGESTONE SPORTS CO.,
LTD.
|
Family ID: |
38446493 |
Appl. No.: |
11/332246 |
Filed: |
January 17, 2006 |
Current U.S.
Class: |
473/384 ;
473/376 |
Current CPC
Class: |
A63B 37/0045 20130101;
A63B 37/008 20130101; A63B 37/0021 20130101; A63B 37/0033 20130101;
A63B 37/0012 20130101; A63B 37/0031 20130101; A63B 37/0018
20130101; A63B 37/0043 20130101; A63B 37/002 20130101; A63B 37/0062
20130101; A63B 37/0064 20130101; A63B 37/0017 20130101; A63B
37/0019 20130101 |
Class at
Publication: |
473/384 ;
473/376 |
International
Class: |
A63B 37/14 20060101
A63B037/14 |
Claims
1. A golf ball comprising, on a spherical surface, numerous dimples
in a plurality of types of differing diameter, wherein the dimples
include smallest size dimples having a diameter of 2.7 mm or less
and largest size dimples having a diameter of 4.3 mm or more, and
at least 50% of the total number of dimples are dimples in which an
arc that connects mutually opposing positions on a wall of the
dimple at a 70% dimple depth level with a deepest position on the
dimple wall has a radius of curvature R of at least 15 mm.
2. The golf ball of claim 1 which has a resilient solid core, a
cover made primarily of polyurethane elastomer that is disposed
outside of the solid core and has thereon said dimples, and an
intermediate layer made primarily of ionomer resin that is disposed
between the cover and the solid core.
3. The golf ball of claim 2, wherein the core has a center portion
and an outer portion which is harder than the center portion, such
that the core center portion and an outside surface of the core
have a JIS-C hardness difference therebetween of at least 25.
4. The golf ball of claim 2, wherein the core has a two-layer
construction composed of an inner layer and an outer layer, said
outer layer having a thickness of 5 to 15 mm.
5. The golf ball of claim 2, wherein the cover is formed to a
thickness of 0.5 to 1.2 mm and has a Shore D hardness of 40 to
55.
6. The golf ball of claim 2, wherein the intermediate layer is
formed to a thickness of 0.9 to 1.7 mm and has a Shore D hardness
of 55 to 70.
7. The golf ball of claim 1, wherein 50 to 97% of the total number
of dimples are dimples in which said arc has a radius of curvature
R of at least 15 mm.
8. The golf ball of claim 1, wherein said arc has a radius of
curvature R of 15 to 40 mm.
9. The golf ball of claim 1, wherein the angle .theta. between a
tangent J drawn at a 30% dimple depth position on the dimple wall
and a circular plane formed by connecting top edge areas of the
dimple is from 4 to 15.degree..
10. The golf ball of claim 1, wherein the total number of dimples
is from 250 to 370.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a golf ball having an
excellent flight performance.
[0002] In the past, to improve both the feel of solid golf balls on
impact and their controllability, such balls were optimized for
properties such as core and cover hardness under high-trajectory
conditions owing to a relatively high spin rate.
[0003] It was later found that a golf ball hit at a low spin and a
high launch angle will travel a longer distance. Accordingly,
greater effort has come to be devoted to increasing the distance of
travel in a manner that is in keeping with these findings. With
recent advances in golfing equipment such as balls and clubs,
designs are being worked out on drivers and other distance clubs
that greatly reduce the amount of backspin taken on by a golf ball
when it is hit.
[0004] Under low-spin conditions, the ball that has been hit will
have a small coefficient of drag, which tends to increase its
distance of travel. Yet, when the dimples that have been used in
earlier golf balls are used unchanged in these more advanced golf
balls, a drop occurs due to insufficient lift in the region of
diminished speed after the ball has reached the highest point of
its trajectory, resulting in a loss of distance.
SUMMARY OF THE INVENTION
[0005] It is thus an object of the invention to provide a golf ball
having a spherical surface on which numerous dimples of differing
diameter are arranged, which ball, owing to the appropriate
selection of the smallest diameter dimples and the largest diameter
dimples and the appropriate selection of the dimple shapes, has an
optimized trajectory when hit and is thus able to advantageous
increase the distance traveled by the ball.
[0006] We have conducted extensive investigations, as a result of
which We have found that by using as the circular dimples arranged
on the surface of a golf ball a plurality of dimples types such
that the largest dimples and the smallest dimples differ markedly
in their diameters, and by appropriately selecting, in
cross-sections of the dimples, the shape of the dimple wall near
the bottom of the dimple, the ball will have an optimized
trajectory and travel farther when hit.
[0007] Accordingly, the invention provides the following golf
balls.
[0008] [1] A golf ball having, on a spherical surface, numerous
dimples in a plurality of types of differing diameter, wherein the
dimples include smallest size dimples having a diameter of 2.7 mm
or less and largest size dimples having a diameter of 4.3 mm or
more, and at least 50% of the total number of dimples are dimples
in which an arc that connects mutually opposing positions on a wall
of the dimple at a 70% dimple depth level with a deepest position
on the dimple wall has a radius of curvature R of at least 15
mm.
[0009] [2] The golf ball of [1] which has a resilient solid core, a
cover made primarily of polyurethane elastomer that is disposed
outside of the solid core and has thereon said dimples, and an
intermediate layer made primarily of ionomer resin that is disposed
between the cover and the solid core.
[0010] [3] The golf ball of [2], wherein the core has a center
portion and an outer portion which is harder than the center
portion, such that the core center portion and an outside surface
of the core have a JIS-C hardness difference therebetween of at
least 25.
[4] The golf ball of [2], wherein the core has a two-layer
construction composed of an inner layer and an outer layer, said
outer layer having a thickness of 5 to 15 mm.
[5] The golf ball of [2], wherein the cover is formed to a
thickness of 0.5 to 1.2 mm and has a Shore D hardness of 40 to
55.
[6] The golf ball of [2], wherein the intermediate layer is formed
to a thickness of 0.9 to 1.7 mm and has a Shore D hardness of 55 to
70.
[7] The golf ball of claim 1, wherein 50 to 97% of the total number
of dimples are dimples in which said arc has a radius of curvature
R of at least 15 mm.
[8] The golf ball of [1], wherein said arc has a radius of
curvature R of 15 to 40 mm.
[9] The golf ball of [1], wherein the angle .theta. between a
tangent J drawn at a 30% dimple depth position on the dimple wall
and a circular plane formed by connecting top edge areas of the
dimple is from 4 to 15.degree..
[10] The golf ball of [1], wherein the total number of dimples is
from 250 to 370.
BRIEF DESCRIPTION OF THE DIAGRAMS
[0011] FIG. 1 is a plan view showing the surface of a golf ball
according to an embodiment of the invention.
[0012] FIG. 2 is an enlarged sectional view of a dimple on the golf
ball of the invention.
[0013] FIG. 3 is a cross-sectional view showing the internal
construction (four-layer construction) of a golf ball according to
an embodiment of the invention.
[0014] FIG. 4 is a plan view showing the surface of the golf ball
in a comparative example.
DETAILED DESCRIPTION OF THE INVENTION
[0015] The invention is described more fully below in conjunction
with the attached diagrams.
[0016] FIG. 1 is a plan view of a golf ball illustrating an
embodiment of the invention, FIG. 2 is a cross-sectional view of
the same golf ball, and FIG. 3 is an enlarged sectional view of a
dimple on the same golf ball.
[0017] Shown in FIG. 1 are a golf ball 1, numerous dimples 2 formed
on the surface of the golf ball, and lands 3. The dimples are
formed in shapes that are circular as seen from directly above.
[0018] FIG. 2 is a detailed view of a dimple region. If a tangent
line L.sub.1 is drawn so as to connect mutually opposing lands 3
and 3' across the dimple 2, the points of intersection between the
tangent L.sub.1 and the dimple 2 are defined as the top edge e. The
top edge e of this dimple 2, like the land 3, lies at a position
farthest away from the center of the golf ball 1. In FIG. 2, the
diameter D.sub.m of the dimple is defined as the diameter of the
circular plane P formed by connecting the top edge e and
circumscribed by the top edge e (i.e., in FIG. 2, the length of the
straight line (above tangent L.sub.1) connecting the mutually
opposed top edges e and e'). Also, the depth D.sub.p of the dimple
is defined as the minimum distance between the plane P (tangent
L.sub.1) and the deepest part B of the dimple
[0019] The golf ball of the invention has numerous dimples in a
plurality of types of differing diameters. Of these dimples, the
smallest dimples 2a have a diameter of 2.7 mm or less, and
preferably 2.0 to 2.7 mm, and the largest dimples 2b have a
diameter of 4.3 mm or more, and preferably 4.3 to 6.0 mm.
[0020] The ratio of the diameter of the largest dimples 2b to the
diameter of the smallest dimples 2a is preferably at least 1.6, and
more preferably from 1.6 to 3.0. By combining in this way dimples
having such a large diameter ratio and optimizing the radius of
curvature, the dimple surface coverage can be increased, enabling
the ball to achieve a longer travel distance.
[0021] In the practice of the invention, the total number of
dimples is preferably from 250 to 370, and more preferably from 280
to 350. It is preferable for the number of dimple types of
differing diameter to be at least three. There is no fixed upper
limit in the number of such dimple types, although from the
standpoint of practicality a maximum of 5 to 20 types is preferred.
The reason is that, within a range in the total number of dimples
disposed on the surface of the ball of 250 to 370, when numerous
large-diameter dimples having a diameter of 4.3 mm or more are used
and the number of dimple types is less than three, it is difficult
to arrange the dimples densely and uniformly on the spherical
surface of the ball. On the other hand, when more than 20 types of
dimple are used, the advantageous effects of the resulting dimple
arrangement are unlikely to justify the associated increases in
mold fabrication and other costs.
[0022] It is preferable for the number of the largest dimples 2a to
be from 12 to 60 and the number of the largest dimples 2b to be
from 120 to 350.
[0023] On the inventive golf ball, at least 50% of the total number
of dimples are dimples in which an arc that connects mutually
opposing positions A and A' on a wall of the dimple at a 70% dimple
depth level and a deepest position B on the dimple wall has a
radius of curvature R of at least 15 mm.
[0024] More specifically, the arc denoted in FIG. 2 by a
dash-dot-dot line represents a ball spherical surface Q that
connects the apices of the land regions which are located farthest
from the center of the ball. In FIG. 2, the cross-sectional shape
which is located between the left and right top edges e and e' of
the dimple and surrounds the base w of the dimple from the walls
thereof may be a circularly or elliptically arcuate shape which is
oriented toward the center of the ball as shown in FIG. 2, a frying
pan-like shape with a flat bottom, or a shape in which the bottom
is convex and rises upward. However, when the arc is formed so as
to connect the mutually opposing positions A and A' on the dimple
wall at a 70% level (d.sub.7) of the dimple depth D.sub.p and the
deepest position B in the dimple, this arc has a radius of
curvature R of 5 to 40 mm, and preferably 7 to 30 mm. At least 50%,
and preferably 50 to 97%, of the total number of dimples are
dimples in which the radius of curvature R is at least 15 mm,
preferably 15 to 40 mm, and more preferably 15 to 30 mm.
[0025] Here, the above positions A, A' and B are shape setting
positions which regulate the dimple shape near the deepest part of
the dimple. That is, the shape near the deepest part of the dimple
must pass successively through these positions A-B-A'. Yet, the
shape of the dimple wall which passes through these positions
A-B-A' is not necessarily limited to an arc of the above radius of
curvature R, and may be modified to a variety of shapes. Hence, the
actual shape of the dimple wall which passes through the positions
A-B-A' may or may not coincide with the above-described arcuate
shape.
[0026] By positionally regulating in this way the shape near the
deepest part of the dimple and by also selecting the dimple
diameter as described above, an increase in the travel distance can
be achieved. If the above-described arc near the deepest part of
the dimple has a radius of curvature R of less than 15 mm, after
the ball that has been hit reaches its highest point on the
parabolic trajectory of its flight, it will undergo a more rapid
decrease in lift, shortening the distance of travel. Moreover, if
the dimples in which this radius of curvature R is at least 15 mm
account for less than 50% of the total number of dimples, owing to
a similarly rapid decrease in lift, the distance traveled by the
ball will fail to increase, making the object of the invention
unattainable.
[0027] Referring again to FIG. 2, letting the surface area of the
above circular plane P be the dimple surface area, to achieve a
good travel distance, it is desirable that the sum .SIGMA.s.sub.R
of this surface area for all the dimples on the ball, expressed as
a ratio with respect to the surface area of the ball were it to be
free of dimples (which ratio is also referred to below as the
"dimple surface coverage"), be preferably at least 70%, and more
preferably at least 75%. Although there is no fixed upper limit in
the dimple surface coverage, the upper limit is generally about
90%.
[0028] Moreover, in FIG. 2, letting the volume of the dimple space
below the circular plane P be the dimple volume v.sub.R, the sum
.SIGMA.v.sub.R of this dimple volume for all the dimples on the
ball, expressed as a ratio with respect to the volume of the ball
were it to be free of dimples, is preferably from 0.70 to 0.85%,
and more preferably from 0.73 to 0.82%. Keeping this ratio in the
above range leaves the ball less subject to the influence of the
dimple cross-sectional shape and enables the distance of travel to
be stabilized.
[0029] The dimple depth D.sub.p is set in a range of preferably
0.05 to 0.3 mm, and more preferably 0.08 to 0.25 mm. It is
especially preferable for the smallest dimples 2a to have a depth
of 0.05 to 0.15 mm, and for the largest dimples 2b to have a depth
of 0.12 to 0.3 mm.
[0030] The top edge e of the dimple and its vicinity may be given
an arcuate shape having a radius of curvature r. It is common
practice to paint the cover of the golf ball so as to form a paint
film thereon. The radius of curvature r in FIG. 2 prior to such
painting is preferably from 0.3 to 3.0 mm. The dimple top edge e
and its vicinity that have been formed to such a radius of
curvature r enable the paint to be applied to the ball at a uniform
thickness in the painting operation, thereby enhancing the
durability of the paint film. The radius of curvature r after
painting is preferably in a range of 0.3 to 10 mm.
[0031] Moreover, in FIG. 2, given the above-described radius of
curvature r near the dimple top edge, the angle .theta. between a
tangent J drawn at a position C on the dimple wall at a 30% level
(depth d.sub.3) of the dimple depth D.sub.p and the above-described
circular plane P (tangent L.sub.1) is preferably from 4 to
15.degree., more preferably from 5 to 12.degree., and most
preferably from 6 to 10.degree..
[0032] In the golf ball of the invention, as shown in FIG. 3, the
center of the ball is formed of a resilient solid core 11 composed
of at least one layer, a cover 12 made primarily of polyurethane
elastomer that is disposed outside of the solid core and has
thereon the above-described dimples, and an intermediate layer 13
made primarily of ionomer resin that is disposed between the cover
12 and the solid core 11.
[0033] Here, it is preferable for the cover thickness t.sub.1 to be
from 0.5 to 1.2 mm and the intermediate layer thickness t.sub.2 to
be from 0.9 to 1.7 mm. The above thicknesses t.sub.1 and t.sub.2
may both be the same or one may be thicker or thinner than the
other, although it is preferable for the cover thickness t.sub.1 to
be relatively thin. Specifically, it is preferably to set the
thickness difference t.sub.2-t.sub.1 in a range of substantially 0
to 1 mm. With regard to hardness, it is preferable for the cover 12
to have a Shore D hardness of 40 to 55, and for the intermediate
layer 13 to have a Shore D hardness of 55 to 70. It is preferable
for the relative hardnesses of the two layers to be such that the
cover 12 has a lower hardness than the intermediate layer 13. If
the Shore D hardnesses of the intermediate layer 13 and the cover
layer 12 are not set within the foregoing ranges, the ball may have
a poor feel when played or an inferior flight performance.
[0034] The solid core is preferably formed to a diameter of 37 to
40 mm. Moreover, it is preferable for the outer portion of the core
to be harder than the center portion, and for the center portion
and the outside surface of the core to have a JIS-C hardness
difference therebetween of at least 25, and especially 25 to 35.
The solid core may have a one-piece construction or, as shown in
FIG. 3, a multi-piece construction composed of an inner layer 11a
and an outer layer 11b. In such a case, the thickness t.sub.3 of
the outer layer 11b may be set at 5 to 15 mm, the thickness
(radius) t.sub.4 of the inner layer 11a may account for the
remaining thickness, and the outer layer may be formed so as to be
harder, within the above-indicated JIS-C hardness range. FIG. 3
also shows the center 11c of the ball.
[0035] When the resilient core is thus formed as a plurality of
layers, by resorting, for example, to the use of a rubber material
in the inner layer 11a and a resin material in the outer layer 11b,
the distinctive properties of the respective materials may be
utilized to optimize the hardness distribution throughout the
resilient core.
[0036] In the resilient solid core 11 used in the invention, the
inner layer 11a and the outer layer 11b may be formed using, for
example, a rubber composition containing suitable ingredients such
as known co-crosslinking agents, organic peroxides, inert fillers
and organosulfur compounds. It is preferable to use polybutadiene
as the base rubber in such a rubber composition. In the case of a
two-layer construction consisting of an inner layer and an outer
layer like that shown in FIG. 3, it is preferable to use
polybutadiene rubber in both.
[0037] The material used to make up the resin cover 12 in the
invention is preferably a thermoplastic polyurethane elastomer. The
material used to make up the intermediate layer 13 in the
invention, while not subject to any particular limitation, may be a
known synthetic resin. For example, preferred use can be made of a
thermoplastic resin or thermoplastic elastomer (e.g., ionomer
resin, thermoplastic polyester elastomer, polyurethane resin,
thermoplastic olefin type elastomer) as the primary material.
[0038] The inventive golf ball can be manufactured by a known
method. Ball properties such as weight and diameter may be suitably
selected according to the Rules of Golf. The ball may generally be
formed to a diameter of not less than 42.67 mm and a weight of not
more than 45.93.
[0039] As described above, the golf ball of the invention, in
addition to having a construction which includes a resilient core
of one or more layers, an intermediate layer and a resin cover,
employing a selected resilient core hardness distribution and a
selected resin cover material, and having optimized intermediate
layer and cover hardnesses, also has a dimple construction and a
dimple arrangement which are optimized. Accordingly, the inventive
ball, through an integral combination of internal features and
dimple parameters, has a significantly increased travel distance,
making it highly advantageous for competitive use.
EXAMPLES
[0040] The following Example of the invention and Comparative
Example are provided by way of illustration and not by way of
limitation.
Example and Comparative Example
[0041] Solid cores having a diameter of 38.2 mm were produced from
the formulations shown in Table 1 by a conventional procedure. The
core in the example of the invention had a two-layer construction
composed of an inner layer and an outer layer, the inner layer
having a diameter of 23.8 mm and the outer layer having a thickness
of 7.2 mm. TABLE-US-00001 TABLE 1 Example Inner Outer Comparative
Ingredients (parts by weight) layer layer Example Polybutadiene
BR730 100 100 100 Zinc acrylate 31 36 31 Zinc oxide 22.6 21.0 22.6
Zinc stearate 5 5 5 Zinc salt of pentachlorothiophenol 0.2 0.2 0.2
2,2'-Methylenebis(4-methyl-6-t- 0.1 0.1 0.1 butylphenol) Dicumyl
peroxide 0.3 0.3 0.3 1,1-Bis(t-butylperoxy)cyclohexane, 0.3 0.3 0.3
40% dilution Notes: Polybutadiene BR730: Produced by JSR
Corporation Zinc acrylate: Produced by Nihon Jyoryu Kogyo Co., Ltd.
Zinc oxide: Produced by Sakai Chemical Industry Co., Ltd. Zinc
stearate: Produced by NOF Corporation
2,2'-Methylenebis(4-methyl-6-t-butylphenol): Produced by Ouchi
Shinko Chemical Industry Co., Ltd. Dicumyl peroxide: Produced by
NOF Corporation 1,1-Bis(t-butylperoxy)cyclohexane, 40% dilution:
Produced by NOF Corporation
[0042] Next, an intermediate layer (1.3 mm) and a cover (0.95 mm)
were each formed by injection molding the formulations shown below,
along with which dimples having the parameters shown in Table 2
were formed.
[0043] The respective materials shown below were used to form the
intermediate layer and the cover in both the example of the
invention and the comparative example.
Intermediate Layer
[0044] H1605: A sodium ion-neutralized ethylene-methacrylic acid
copolymer ionomer produced by DuPont-Mitsui Polychemicals Co., Ltd.
Cover [0045] Pandex T8295: An MDI-PTMG type thermoplastic
polyurethane produced by DIC Bayer Polymer, Ltd. [0046] Pandex
T8260: An MDI-PTMG type thermoplastic polyurethane produced by DIC
Bayer Polymer, Ltd. [0047] Crossnate EM-30: An isocyanate produced
by Dainichi Seika Colour & Chemicals Mfg. Co., Ltd.
[0048] The cover material was prepared by blending 18 parts by
weight of Crossnate EM-30 into a mixture of 50 parts by weight of
Pandex T8295 and 50 parts by weight of Pandex T8260. TABLE-US-00002
TABLE 2 Example Comparative Example Type D.sub.1 D.sub.2 D.sub.3
D.sub.4 D.sub.5 D.sub.6 D.sub.1 D.sub.2 D.sub.3 D.sub.4 D.sub.5
Number of 12 234 60 6 6 12 288 60 12 12 60 dimples n Diameter (mm)
4.6 4.4 3.8 3.5 3.4 2.6 3.9 3.8 3.4 2.9 2.4 Depth d (mm) 0.14 0.14
0.14 0.13 0.13 0.10 0.15 0.15 0.14 0.13 0.10 R (mm) 22 19 14 11 10
8 13 13 11 9 8 .theta. (.degree.) 7 7 8 8 8 8 9 9 9 10 9 Total
number 330 432 of dimples .SIGMA.n .SIGMA.v.sub.R (mm.sup.3) 313
321 .SIGMA.s.sub.R (mm.sup.2) 4614 4564 Total volume 0.77 0.79
ratio (%) Total surface 81 80 area ratio (%) Notes: R: The radius
of curvature of the arc that passes through positions A and A' on
the dimple wall at 70% of the dimple depth (d.sub.7). .theta.: The
angle between a tangent J at a position D on the dimple wall at 30%
of the dimple depth (d.sub.3) and a circular plane P.
.SIGMA.v.sub.R: Total volume of the dimples. .SIGMA.s.sub.R: Total
surface area of the dimples. Total volume ratio: Ratio of total
volume of all dimples on the ball to the volume of the ball were
the surface to be free of dimples. Total surface area ratio: Ratio
of total surface area of all dimples on the ball to the surface
area of the ball were the surface to be free of dimples.
Ball Construction and Test Results
[0049] Table 3 shows the ball constructions in the example of the
invention and the comparative example, and also shows the results
of distance tests conducted on these balls. In the distance test,
each ball was hit at a head speed of 45 m/s with a club (W#1)
mounted on a swing robot, and both the carry and the total distance
were measured. TABLE-US-00003 TABLE 3 Comparative Example Example
Ball Diameter (mm) 42.7 42.7 Resilient Radius (mm) 19.1 19.1 core
Construction two-piece one-piece (A) Center hardness 61 66 (JIS-C
hardness) (B) Outer surface hardness 89 77 (JIS-C hardness) (B) -
(A) 28 11 Intermediate Thickness t.sub.2 (mm) 1.30 1.30 layer Shore
D hardness 64 64 Cover Thickness t.sub.1 (mm) 0.95 0.95 Shore D
hardness 53 53 Test results Carry (m) 223 219 Total distance (m)
244 240 Notes: (1) In the two-piece core construction in the
example of the invention, the core had an outer layer thickness
t.sub.3 of 7.2 mm and an inner layer radius t.sub.4 of 11.95 mm.
The core radius in the comparative example was 18.65 mm. (2) The
Shore D hardnesses are values obtained by measurement in accordance
with ASTEM-D2240.
* * * * *